1. Field of the Invention
The present invention relates to an exposure control system of a still camera and, more particularly, to an aperture size control device for controlling the size of an aperture during a photographic exposure.
2. Description of the Prior Art
According to a prior art exposure control system, an aperture size is initially determined in consideration of desired shutter speed, film speed and the brightness of an object scene to be photographed. When the aperture size is once determined, it is maintained constant until one exposure operation is completed.
When photographing an object scene under normal daylight, an auxiliary flash light is often used, for example when the main object is shaded, to ensure development of the fine details of the object. In such a case, photographing by a prior art exposure control system is carried out in the following manner. Before the exposure, the aperture size is set to provide an appropriate exposure for a background, or the surrounding objects to be photographed, such as mountains, under daylight. Then, when the shutter is released, a photographic film surface is exposed with light rays that pass through the set aperture size. During and within the exposure period, a flash light is emitted from a flash light device, which is of a type that can change the amount of light emission. The emitted flash light is expected to primarily brighten the main object to be photographed, e.g., a man with a background of mountains. The flash light reflected from the man is exposed on the film surface through the set aperture, and the flash light further reflected from the film surface is measured within the camera. When the measured amount of light from the film surface reaches a certain level, the emission of flash light is stopped to provide an appropriate exposure for the man. Thereafter, the shutter closes. By the above-described manner, it is possible to provide an appropriate exposure both to the main object and the surrounding objects.
According to the prior art exposure control system, however, there are certain disadvantages as described hereinafter. In the above given example, the background, which is mountains, is relatively bright and, therefore, the aperture size should be set to a relatively small size, such as f-stop 8. When the flash light device has a maximum available guide number of, e.g., 32, its shooting range for the f-stop 8 is 4 meters or less. Therefore, when the man is located further than 4 meters from the camera, his image will be underexposed even if the flash light device emits the maximum light amount.
On the contrary, when the background is relatively dark, such as night scenery, the aperture size is set to a relatively large size, such as f-stop 1.4. When the flash light device has a minimum available guide number of, e.g., 2, its shooting range for the f-stop 1.4 is 1.4 meters or more. Therefore, when the man is located close to the camera less than 1.4 meters, his image will be overexposed even if the flash light device emits the minimum light amount. Furthermore, the depth of field will be very shallow.
Thus the prior art is still seeking to provide a camera that is capable of providing a full range of photographic capabilities to permit artistic and creative pictures to be taken even under adverse lighting conditions.